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If \(y = \sec(\tan^{-1}x)\) ,then \(\frac{dy}{dx}\) at \(x = \sqrt{3}\) is equal to

  • A.\(\frac{2\sqrt{3}}{3}\)
  • B.\(\frac{1}{2}\)
  • C.2
  • D.\(\frac{\sqrt{3}}{2}\)
  • E.\(2\sqrt{3}\)

Answer: D

\(\frac{dy}{dx} =\) \(\frac{\sqrt{3}}{2}\).

If \(\theta = \tan^{-1}x\), then \(\sec\theta = \sqrt{1 + x^{2}}\), so \(y = \sqrt{1 + x^{2}}\) and

\[ \begin{aligned} \frac{dy}{dx} &= \frac{x}{\sqrt{1 + x^{2}}} \\ &= \frac{\sqrt{3}}{\sqrt{4}} \\ &= \frac{\sqrt{3}}{2} \end{aligned} \]

at \(x = \sqrt{3}\). \(\frac{1}{2}\) is \(\frac{1}{\sqrt{1 + x^{2}}}\), and 2 is the value of \(y\) itself; the other options do not follow.

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